Perform a wide variety of building and equipment maintenance work and supplementary work on HVAC systems, including air conditioners, air handler units, exhaust systems, chillers, boilers, humidifiers, air distribution systems, water treatment, air filters, building automation systems, steam systems, etc. About BAE Systems Space & Mission Systems BAE Systems, Inc. is the U.S. subsidiary of BAE Systems plc, an international defense, aerospace and security company which delivers a full range of products and services for air, land and naval forces, as well as advanced electronics, security, information technology solutions and customer support services.